1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to an LCD device having advantages in weight and thickness and being flexible.
2. Discussion of the Related Art
As the society has entered in earnest upon an information age, flat panel display devices, which have excellent capabilities of a thin profile, light weight and low power consumption, and so on, are introduced. For example, the flat panel display devices include an LCD device, a plasma display panel (PDP) device, a vacuum fluorescent display (VFD) device and an electroluminescent display (ELD) device.
Among these devices, LCD devices are widely used for notebook computers, monitors, TV, and so on instead of a cathode ray tube (CRT), because of their high contrast ratio and characteristics adequate to display moving images.
The LCD device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by application of an electric field across the liquid crystal molecules. As the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.
Since the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics such as high resolution and display of moving images, the AM-LCD device has been widely used.
FIG. 1 is a schematic cross-sectional view of the related art LCD device. In FIG. 1, the LCD device 1 includes first and second substrates 5 and 10, a liquid crystal layer 15 and a backlight unit 90. The first and second substrates 5 and 10 face each other, and the liquid crystal layer 15 is interposed between the first and second substrates 5 and 10. The backlight unit 90 is disposed under the first substrate 5. A combination of the first and second substrates 5 and 10 and the liquid crystal layer 15 may be called as a liquid crystal panel 30. For example, each of the first and second substrates 5 and 10 may be formed of a transparent glass.
On the first substrates 5, a pixel region P, which is defined by gate and data lines (not shown) crossing each other, and a switching region S, where a thin film transistor (TFT) T as a switching element is formed, are defined. The TFT T is disposed at a crossing portion of the gate and data lines. The TFT T includes a gate electrode 25, a gate insulating layer 45, a semiconductor layer 40, a source electrode 32 and a drain electrode 34. The semiconductor layer 40 may include an active layer of intrinsic amorphous silicon and an ohmic contact layer of impurity-doped amorphous silicon.
A passivation layer 55 is formed on the TFT T and includes a drain contact hole DCH exposing the drain electrode 34. In addition, a pixel electrode 70 connected to the drain electrode 34 through the drain contact hole DCH is formed on the passivation layer 55 in each pixel region P. For example, the pixel electrode 70 may be formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO).
On the second substrate 10, a black matrix 12 for shielding the gate and data lines and the TFT T on the first substrate is formed. A color filter layer 16 including red (R), green (G) and blue (B) sub-color filters 16a, 16b and 16c is formed on the black matrix 12. The sub-color filters 16a, 16b and 16c correspond to each pixel region P. In addition, a common electrode 75 is formed on the color filter layer 16. For example, the common electrode 75 may be formed of a transparent conductive material such as ITO and IZO. Although not shown, first and second alignment layers may be formed on the pixel electrode 70 and the common electrode 75, respectively.
Liquid crystal molecules L in the liquid crystal layer 15 is driven by a vertical electric field induced between the pixel and common electrodes 70 and 75 such that light transmissivity is controlled. The light is provided from the backlight unit 90. Color images are displayed due to the color filter layer 16.
The backlight unit 90 includes one of a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL) and a light emitting diode (LED) as a light source. The backlight unit 90 further includes members depending on a kind of the light source. For example, the backlight unit 90 may include a reflective sheet and an optical sheet.
Recently, a flexible substrate, for example, a plastic or a flexible metal substrate, is used for each of the first and second substrates 5 and 10 to obtain a flexible LCD device. Unfortunately, the backlight unit 90 is formed of rigid material, for example, a glass substrate, such that there is a limitation to provide a flexible LCD device.